The present invention relates to a method of manufacturing a structural body using a friction stir welding method; and, for example, the invention relates to a manufacturing method suitable for the manufacture of a car body of a railway vehicle.
Friction stir welding is a method wherein a round rod (called a "rotary tool"), which is inserted into a welding joint, is rotated and moved along the welding joint so that the welding joint is heated, softened and solid-fluidized, whereby a solid phase welding occurs.
The rotary tool comprises a small diameter portion which is inserted into the welding joint, and a large diameter portion which is positioned outside of the small diameter portion. The small diameter portion and the large diameter portion of the rotary tool have the same axis of rotation. A boundary between the small diameter portion and the large diameter portion of the rotary tool is inserted slightly into the welding joint. The rotary tool is inclined toward the rear relative to the advancing direction of the welding.
A car body of a railway vehicle is constituted by carrying out a friction stir welding of plural extruded frame members. The longitudinal direction of the extruded frame member is directed in the longitudinal direction of the car body, and the width of the extruded frame member is arranged in the direction of the height of the car body. To a side face of the car body with the above-stated construction, an opening, such as a door or window, is typically provided by cutting-out a portion of the extruded members.
The above-stated technique is disclosed in Japanese application patent laid-open publication No. 09-309164 (EP 0797043A2).
Since the height of a window of a car body is typically larger than the width of an extruded frame member, the window is formed by an opening cut into two or three frame members. For this reason, the extruded frame members in which a cut-off portion is provided are substantially aligned to form the window and then joined by welding. A friction stir welding apparatus for manufacturing a car body comprises a bed for mounting plural extruded frame members and a gantry disposed over the bed and from which plural rotary tools are suspended. By controlled movement of the gantry, the plural rotary tools are moved so that plural extruded frame members can be welded simultaneously.
In a case where the plural extruded frame members are welded simultaneously using plural rotary tools which are suspended from a gantry, when a first rotary tool reaches a position where a window is located, this rotary tool is withdrawn from the extruded frame member, and the friction stir welding being performed by this rotary tool is stopped. Meanwhile, a second rotary tool for welding a portion where a window does not exist is allowed to continue the friction stir welding as it is. When the first rotary tool is moved to a position at the other end of the window, this first rotary tool is inserted once again into the weld joint and the friction stir welding is resumed.
When this process is carried out, by removing the first rotary tool from the welding joint at one side of the window a nd then re-inserting into the welding joint at the other side of the window, a defect in the welding can be generated easily. Further, at an initial time during the start of the friction stir welding since the temperature of the welding joint has not yet been raised, a large insertion force is required for inserting the rotary tool into the welding joint.
In addition to the above, since the rotary tool is moved while it is inserted into the welding joint, a slant force is generated against a bearing member of the rotary tool. For this reason, the bearing member is required to be large in size, and a problem with the life expectancy of the rotary tool occurs.